Power semiconductor device

ABSTRACT

The present invention relates to a power semiconductor device comprising a switching power semiconductor element, and a free wheeling diode in anti-parallel connection to the switching power semiconductor element. The power semiconductor is characterized in that a reverse electrode of the switching power semiconductor element and a reverse electrode of the free wheeling diode are bonded and mounted on a circuit pattern formed on the main surface of the first substrate, and that a circuit pattern, which is so formed on the main surface of the second substrate as to oppose a surface electrode of the switching power semiconductor element and a surface electrode of the free wheeling diode, is connected to the surface electrodes of the switching power semiconductor element and the free wheeling diode through connective conductors to be soldered, respectively.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 11/029,379, filed Jan. 6, 2005, now U.S. Pat. No. 7,535,076, whichin turn claims the benefit of patent applications No. 2004-1848 filed inJapan on Jan. 7, 2004, the entire contents of each of which are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power semiconductor device.

2. Description of the Related Art

One of conventional power semiconductor devices is shown in FIG. 13.

Disposed on the metallic base board (2) is an insulating substrate (4)of ceramics having metal-plated circuit patterns on both sides, andmounted on the insulating substrate (4) are a switching powersemiconductor element (6) such as IGBT, MOSFET or the like and a freewheeling diode (8). The switching power semiconductor element (6) andthe free wheeling diode (8) are connected to a casing (18) havingexternal terminals built therein (an insert casing), through theexternal terminals. The switching power semiconductor element (6) suchas IGBT is so disposed that the upper side (surface) thereof serves asan emitter face and the lower side (reverse) thereof, as a collectorface. The free wheeling diode (8) is so disposed that the upper side(surface) thereof serves as an anode face, and the lower side (reverse)thereof, as a cathode face. The circuit as a whole comprises a patternformed on the insulating substrate (4) and wires (20), and is connectedto the casing (18). Gel (or a resin, or gel and a resin) (36) isinserted into the casing (18) so as to protect the element and thecircuit, and the casing (18) is covered with a lid.

In this power semiconductor device, the connection of the emitter faceof the switching power semiconductor element (6) is made through thewires (20), and this connection method arises the following problems.

Firstly, there is a limit in the capacity of a current since the wire(20) is thin. In practical use, a required capacity of current isensured for a main circuit by using thicker wires, or increasing thenumber of wires (20). However, this method requires spaces for wirebonding, and therefore has a limit in miniaturization of the elementsand the device. Secondly, the circuit resistance becomes larger becauseof the use of the thin wires (20). While this problem also can be solvedby using thicker wires or increasing the number of the wires (20), thereare limits as mentioned above. Thirdly, heat is locally accumulated,since a current is concentrated on the joints of the wires on theswitching power semiconductor element (6). While the concentration ofheat is reduced by decentralizing the joints of the wires on theelement, heat is not completely decentralized. Fourthly, the gate mayoscillate when a short circuit occurs in the semiconductor device. Inthe power semiconductor device, a wire (20) is bonded to each of theemitter cells of the switching power semiconductor element (6), and thecells are connected to one another through the pattern formed on theinsulating substrate (4) to which the wires (20) are bonded. Suchconnection causes unbalance between each of the cells, and thus, thegate oscillates when a short circuit occurs in the semiconductor device.As a result, the device may be destructed or may cause malfunction. Itmay be possible to solve this problem by direct stitch connection ofeach of the cells through the wires. However, the number of operationsfor wire bonding is increased, and the area of the device for such wirebonding is also increased. As a result, there still remain similarlimits to the first problem. Fifthly, spaces for bonding the wires areneeded.

The foregoing are main problems in relation to the wires (20). There arefurther problems in relation to heat radiation. In the conventionalsemiconductor device, heat radiation is carried out by applying greaseto the reverse side of the base board and screwing heat radiation fins.In this case, only one side of the device is used for heat radiation.

JP-A-10-56131 discloses a technique in which connection of mainelectrodes is made through a plurality of bumps in a IGBT module havingcircuit patterns on the upper and lower sides thereof. JP-A-8-8395discloses a technique in which an element analogous to the connectiveconductor is used. JP-A-10-233509 describes an example of a devicehaving a plurality of bumps provided therein. JP-A-6-302734 discloses atechnique in which two substrates are connected to each other through aspring. JP-A-8-17972 discloses a technique for embedding poles and metalballs in bumps for use in connection of a package mother board.JP-A-2002-16215 and JP-A-2002-76254 disclose IPMs each of which uses twolead frames, i.e. upper and lower lead frames.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a powersemiconductor device improved as follows: the current capacity of themain circuit is improved, and the circuit resistance is decreased; heatcan be decentralized on the element; and the oscillation of gate due tothe unbalance of emitter cells can be prevented.

The present invention is developed in order to achieve the above object.A power semiconductor device according to a preferred embodiment of thepresent invention comprises a switching power semiconductor element, anda free wheeling diode in antiparallel connection to the switching powersemiconductor element, and this power semiconductor device ischaracterized in that a reverse electrode of the switching powersemiconductor element and a reverse electrode of the free wheeling diodeare bonded and mounted on a circuit pattern formed on a main surface ofthe first substrate; and that a circuit pattern, which is so formed on amain surface of the second substrate as to oppose a surface electrode ofthe switching power semiconductor element and a surface electrode of thefree wheeling diode, is connected to the surface electrodes of theswitching power semiconductor element and the free wheeling diodethrough connective conductors to be soldered, respectively.

According to the present invention, the current capacity of the maincircuit can be greatly improved, and the circuit resistance can bedecreased. In addition, heat can be decentralized on the element; theoscillation of the gate due to the unbalance of the emitter cells iseffectively prevented; and the miniaturization of the device becomespossible. Further, heat radiation from the upper side and the lower sideof the power semiconductor device also becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a power semiconductor device according to the firstembodiment of the present invention;

FIG. 2 shows a power semiconductor device according to the secondembodiment of the present invention;

FIG. 3 shows a power semiconductor device according to the thirdembodiment of the present invention;

FIG. 4 shows a power semiconductor device according to the fourthembodiment of the present invention;

FIG. 5 shows a power semiconductor device according to the fifthembodiment of the present invention;

FIG. 6 shows a diagram illustrating the insertion of a gel-likeinsulating and heat resistant filler between the first substrate and thesecond substrate;

FIG. 7 shows a power semiconductor device according to the sixthembodiment of the present invention;

FIG. 8 shows another power semiconductor device according to the sixthembodiment of the present invention;

FIG. 9 shows a power semiconductor device according to the seventhembodiment of the present invention;

FIG. 10 shows another power semiconductor device according to theseventh embodiment of the present invention;

FIG. 11 shows a power semiconductor device according to the eighthembodiment of the present invention;

FIG. 12 shows another power semiconductor device according to the eighthembodiment of the present invention; and

FIG. 13 shows a conventional power semiconductor device according to theprior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments according to the present inventionwill be illustrated with reference to the accompanying drawings.

Embodiment 1

FIG. 1, consisting of FIGS. 1(1) to 1(3), shows a power semiconductordevice according to Embodiment 1 of the present invention. FIG. 1(1)shows a top plan view of a first substrate described below; FIG. 1(2), abottom view of a second substrate described below; and FIG. 1(3), alongitudinal sectional view of the power semiconductor device. In thispower semiconductor device, a switching power semiconductor element (6)and a free wheeling diode (8) are mounted on the first substrate (24).The emitter face of the switching power semiconductor element (6) andthe anode face of the free wheeling diode (8) are connected to thesecond substrate (26) which is an insulating substrate having a circuitpattern formed thereon, through connective conductors (22) (balls asseen in Figure). Herein, the switching power semiconductor element (6)is a semiconductor such as IGBT, MOSFET or the like. The switching powersemiconductor element (6) and the free wheeling diode (8) have reverseelectrodes 9 and surface electrodes 7, respectively. The first andsecond substrates (24, 26) have circuit patterns 5, respectively. InFIG. 1(1), reference numerals (10, 12) indicate main current terminals,and reference numerals (14) and (16) indicate a signal terminal (gate)and a signal terminal (emitter), respectively. The main currentterminals (10, 12) and the signal terminals (14, 16) are also indicatedas external terminals (11).

As shown in FIG. 1(3), a heat sink (32) as a heat radiation portion isbonded to the underside of the first substrate (24). The heat sink (32)may be bonded to the upper side of the second substrate. In case wheresome problem in strength arises because of the direct exposure of theinsulating substrate to an external as seen in FIG. 1(3), a base boardis provided on the underside of the device, or a part of the device iscoated, or covered with a casing.

The connective conductors (22) and the components of the device may beconnected by soldering, ultrasonic bonding or pressure welding. InEmbodiment 1, all the components are mounted on the first substrate(24). This is advantageous, because difficulties in production can beavoided, so that the productivity is improved. The connective conductors(22) are allowed to have flexibility after the device is assembled, sothat stresses applied to the connective conductors (22) can be absorbed.

A gel-like, insulating and heat resistant filler (36) (not hatched foreasy recognition of the drawing) is inserted between the first substrate(24) and the second substrate (26). As shown in FIG. 6, the three sidesof the space between the first substrate (24) and the second substrate(26) is sealed with an adhesive or a partitioning member (34) so thatthe filler (36) can be inserted from an opening left to remain. Thefiller may be inserted from the bases of the three sides but not theopening, using a syringe or the like.

Embodiment 1 provides the following advantages. In general, the currentcapacity of a conductive material is in proportion to the sectional areathereof, and the electric resistance thereof is in inverse proportion tothe sectional area thereof. To increase the current capacity of acircuit and to decrease the electric resistance thereof, the sectionalarea of the conductive material should be increased. However, the areaof the emitter face is limited in the semiconductor element of the powersemiconductor device, and thus, the sectional area of all the wires(=the sectional area of one wire×the number of wires) can not beunrestrictedly increased. In addition, such wire connection unavoidablyrequires dead spaces for allowing connecting operations. In this pointof view, the use of the connective conductors (22) as in Embodiment 1dispenses with such dead spaces. In this regard, the connection throughwires was compared with the connection through connective conductors,provided that the wires and the connective conductors were made of thesame material. Then, it is found that the latter case can have asectional area substantially two or more times larger than that of theformer case.

The first substrate (24) and the second substrate (26), opposed to eachother, are connected to each other with a relatively short distancetherebetween, and therefore, the electrical and thermal resistancesbecome smaller in accordance with the distance. How much this distancecan be decreased depends on the degree of necessity of insulationbetween the two substrates. In this embodiment, it is considered thatthis distance can be decreased to about 2 mm at a rated voltage of about3.3 V because of the insertion of the insulating filler.

Wires are generally made of aluminum (Al) for the convenience ofprocessing. On the other hand, the connective conductors (22) used inthe first embodiment can be made without taking into account suchprocessing convenience, and thus can be made of copper (Cu) which hashigher electric and heat conductivities than Al.

As described above, since the insulating substrate having the circuitpattern formed thereon is connected through the connective conductors inEmbodiment 1, the current capacity of the main circuit can be greatlyimproved, and the circuit resistance can be decreased. Further, thepractical area for allowing the connection of the emitter cells arerelatively large, and therefore, the emitter cells can be connected tothe circuit pattern with a relatively short distance between them.Consequently, heat decentralization on the semiconductor element isimproved, and the oscillation of the gate due to the unbalance of theemitter cells can be prevented. In addition, the spaces required forconnecting the wires to the circuit pattern can be decreased, and thus,the area of the plane surfaces of a whole of the device can bedecreased. The height of the device is not so increased in Embodiment 1,because the height of the wire is originally needed in the powersemiconductor device.

Further, by mounting heat sinks on both the upper side and the lowerside of the device, the heat radiation effect can be improved.

Embodiment 2

FIG. 2, consisting of FIGS. 2(1) to 2(3), shows a power semiconductordevice according to Embodiment 2 of the present invention. Since thepower semiconductor device according to the second embodiment issubstantially the same as that according to the first embodiment, thedescription thereof is saved by denoting the like components with thelike reference numerals, and thus, the difference of this embodiment ismainly described. FIG. 2(1) shows a top plan view of a first substrate;FIG. 2(2), a bottom view of a second substrate; and FIG. 2(3), alongitudinal sectional view of the device, as well as FIG. 1.

The power semiconductor device according to Embodiment 2 comprises, asthe second substrate (26), an insulating substrate which has, thereon, acircuit pattern provided with connective projections (38) but not theconnective conductors. The connective projections (38) are made of aconductive material, and are connected to the emitter face of theswitching power semiconductor element (6) and the anode face of the freewheeling diode (8) on the first substrate (24).

Embodiment 2 provides the following advantages. In Embodiment 1, it isneeded that the connective conductors are connected to both thesemiconductor element and the insulating substrate having the circuitpattern formed thereon. Therefore, a larger number of steps arerequired, and it is anticipated that some difficulties may arise as thecase may be. On the other hand, in Embodiment 2, the insulatingsubstrate having, thereon, the circuit pattern provided with theconnective projections is used to thereby save the production steps andalso to improve the reliability of the power semiconductor device.

Embodiment 3

FIG. 3, consisting of FIGS. 3(1) to 3(3), shows a power semiconductordevice according to Embodiment 3 of the present invention. Since thepower semiconductor device according to Embodiment 3 is substantiallythe same as those according to Embodiment 1 and Embodiment 2, thedescription thereof is saved by denoting the like components with thelike reference numerals, and thus, the difference of this embodiment ismainly described. FIG. 3(1) shows a top plan view of a first substrate;FIG. 3(2), a bottom view of a second substrate; and FIG. 3(3), alongitudinal sectional view of the device, as well as FIGS. 1 and 2.

The power semiconductor device according to Embodiment 3 shown in FIG. 3comprises an insulating substrate which has, thereon, a circuit patternprovided with connective projections as in Embodiment 2 (i.e. a secondsubstrate (26)), and also uses connective conductors (22). That is, theemitter face of the switching power semiconductor element (6) and theanode face of the free wheeling diode (8) on the first substrate (24)are connected to the circuit pattern formed on the insulating substrateas the second substrate (26) through the conductive projections (3) onthe circuit pattern and the connective conductors (22).

In Embodiment 3, by concurrently using the connective projections andthe connective conductors, the distance between the first substrate (24)and the second substrate (26) opposed to each other, and the arearequired for the connection of both the substrates can be independentlyadjusted. Therefore, an optimal designing for the device can be made,taking into account a current capacity, quantity of heat and stresses.

Embodiment 4

FIG. 4, consisting of FIGS. 4(1) to 4(3), shows a power semiconductordevice according to Embodiment 4 of the present invention. Since thepower semiconductor device according to Embodiment 4 is substantiallythe same as those according to Embodiment 1 to Embodiment 3, thedescription thereof is saved by denoting the like components with thelike reference numerals, and thus, the difference of this embodiment ismainly described. FIG. 4(1) shows a top plan view of a first substrate;FIG. 4(2), a bottom view of a second substrate; and FIG. 4(3), alongitudinal sectional view of the device, as well as FIG. 1.

The power semiconductor device according to Embodiment 4 shown in FIG. 4is in accordance with any of Embodiment 1 to Embodiment 3, except that aconductive portion is formed on a part of the second substrate (26) soas to electrically connect the surface and the reverse of the substrateto each other, and that a circuit pattern is formed on the reverse (orthe outer surface) of the substrate. A control circuit (40) forcontrolling the driving of the switching power semiconductor element (6)is mounted on the circuit pattern formed on the reverse of the secondsubstrate (26).

Arranged as above, a driving control unit can be directly mountedwithout the need of a separate printed board or the like. Therefore, thenumber of components is decreased, and the productivity is improved.Further, the inductance can be decreased by disposing the drivingcontrol unit in the vicinity of the switching power semiconductorelement (6). As a result, more correct control becomes possible.

Embodiment 5

FIG. 5, consisting of FIGS. 5(1) to 5(3), shows a power semiconductordevice according to Embodiment 5 of the present invention. Since thepower semiconductor device according to Embodiment 5 is substantiallythe same as those according to Embodiment 1 to Embodiment 4, thedescription thereof is saved by denoting the like components with thelike reference numerals, and thus, the difference of this embodiment ismainly described. FIG. 5(1) shows a top plan view of a first substrate;FIG. 5(2), a bottom view of a second substrate; and FIG. 5(3), alongitudinal sectional view of the device, as well as FIG. 1.

The power semiconductor device according to Embodiment 5 shown in FIG. 5is in accordance with any of Embodiment 1 to Embodiment 4, except thatat least the first substrate (24) is a ceramic insulating substrate, andthat a heat sink (32) divided into a plurality of portions is bonded tothe reverse of the ceramic insulating substrate.

Arranged as above, the heat radiation efficiency is improved, and thecracking of the ceramic substrate due to heating can be prevented, sincethe heat sink is divided into the plurality of portions to therebydeconcentrate a stress.

Otherwise, the heat sink divided as above may be formed integrally withthe first substrate (24). By doing so, the productivity can be improved,and an increase in thermal resistance at the connections due to voids,cracks or the like can be prevented.

Embodiment 6

FIGS. 7 and 8 show power semiconductor devices according to Embodiment 6of the present invention. FIG. 7(1) or 8(1) shows a top plan view of afirst lead frame (described later); FIG. 7(2) or 8(2), a bottom view ofa second lead frame (described later); and FIG. 7(3) or 8(3), alongitudinal sectional view of the device, as well as FIGS. 1 to 5.

Also, this power semiconductor device comprises a switching powersemiconductor element (6), and a free wheeling diode (8) inanti-parallel connection to the switching power semiconductor element(6). However, both the components are mounted on the lead frame (thefirst lead frame (28)) but not on the insulating substrate. That is, areverse electrode of the switching power semiconductor element (6) and areverse electrode of the free wheeling diode (8) are bonded on the mainsurface of the first lead frame (28). Simultaneously, a surfaceelectrode of the switching power semiconductor element (6) and a surfaceelectrode of the free wheeling diode (8) are connected to projections(38) which are formed by projecting such parts of the surface of thesecond lead frame (30) that oppose the surface electrodes of theswitching power semiconductor element (6) and the free wheeling diode(8). A whole of this structure is shaped by transfer-molding a resin.

As compared with the power semiconductor device according to Embodiment1, the dielectric strength of the power semiconductor device accordingto Embodiment 6 is lower. However, this device can be produced at lowercost and in higher productivity, since the lead frames which areinexpensive and are easily shaped are used. Further, by making externalterminals of the lead frames, the number of the components can bedecreased, and thus, the productivity can be improved.

In the power semiconductor device shown in FIG. 7, a plurality ofconnective projections (38) are provided relative to one element, andthereby, wiring for the gate on the surface of the element can beavoided. Further, such a plurality of connective projections areintended to relax a stress. In the power semiconductor device shown inFIG. 8, the connective projections (38) are formed as having flat facesto thereby increase the connected area. By doing so, the concentrationof current on the element can be prevented, and the heat radiationefficiency can be improved.

Embodiment 7

FIG. 9, consisting of FIGS. 9(1) to 9(3), shows a power semiconductordevice according to Embodiment 7 of the present invention. Since thepower semiconductor device according to Embodiment 7 is substantiallythe same as that according to Embodiment 6, the description thereof issaved by denoting the like components with the like reference numerals,and thus, the difference of this embodiment is mainly described. FIG.9(1) shows a top plan view of a first lead frame; FIG. 9(2), a bottomview of a second lead frame; and FIG. 9(3), a longitudinal sectionalview of the device, as well as FIGS. 7 and 8.

In the power semiconductor device according to Embodiment 7, both of thefirst lead frame (28) and the second lead frame (30) are shaped in theform of flat plates. A plurality of connective conductors (22) aresoldered at predetermined positions on the main surface of the secondlead frame (30) which opposes the first lead frame. The plurality ofconnective conductors are allowed to correspond to the surface electrodeof the switching power semiconductor element (6) and the surfaceelectrode of the free wheeling diode (8) and are soldered thereto. Inother words, the upper and lower lead frames are connected through theconnective conductors (22) but not connective projections.

As compared with Embodiment 6, the number of the components is increasedin the power semiconductor device according to Embodiment 7, while theshape and material of the connective portions can be more freelyselected, and therefore, the circuit resistance can be decreased, andthe reliability of the device can be improved.

In the power semiconductor device according to Embodiment 7, a controlcircuit (40) for controlling the driving of the switching powersemiconductor element (6) may be mounted on the reverse of the secondlead frame (30), the main surface of which is opposed to the first leadframe (28), as shown in FIG. 10.

Further, a multi-layer printed board or a through hole board may be usedin place of the second lead frame, and a control circuit for controllingthe driving of the switching power semiconductor element (6) may bemounted on such a board.

By mounting the control circuit (40) as above, a driving control unitcan be directly mounted without the need of a separate printed board.Thus, the number of the components can be decreased, and theproductivity can be improved. Further, by disposing the driving controlunit in the vicinity of the switching power semiconductor element, theinductance can be decreased, and thus, more correct controlling can berealized.

Embodiment 8

FIGS. 11 and 12 show power semiconductor devices according to Embodiment8 of the present invention. FIG. 11 consists of FIGS. 11(1) to 11(4),wherein FIG. 11(1) shows a longitudinal sectional view of the device;FIG. 11(2), a bottom view of a third lead frame; FIG. 11(3), a top planview of a second lead frame; and FIG. 11(4), a top plan view of a firstlead frame. FIG. 12 consists of FIGS. 12(1) to 12(5), wherein FIG. 12(1)shows a longitudinal sectional view of the device; FIG. 12(2), a bottomview of a fourth lead frame; FIG. 12(3), a top plan view of a third leadframe; FIG. 12(4), a bottom view of a second lead frame; and FIG. 12(5),a top plan view of a first lead frame.

The power semiconductor devices shown in FIGS. 11 and 12 are provided byapplying any of Embodiment 1 to 7, and at least three lead frames (orinsulating substrates), but not two lead frames, are used in either ofthese embodiments. The devices also include mold resin (42), maincurrent terminals (44, 46, 48), signal terminals (50, 52, 54, 56), thirdlead frame (58), fourth lead frame (60), and insulating plate (62).

In a conventional power semiconductor device, when the number ofelements to be mounted is increased, the area for mounting them isunavoidably spread in two dimensional directions on a plane, so that thearea of such plane portions is increased in proportion to the number ofthe elements. By contrast, in this embodiment, the components can bedisposed in three dimensional directions, and thus, the area of theplane portions of the device can be largely decreased. In this regard,it is considered that the height of the device becomes higher in inverseproportion to the decreased area. However, since a considerable heightis required for wire connection in the conventional device, the heightof the device of this embodiment is not so largely increased as comparedwith the height of the conventional device.

This embodiment makes it possible to not only reduce the plane area andthe circuit resistance, but also provide the following effect. In casewhere this embodiment of the present invention comprises an invertercircuit, it is possible to form one arm, using three lead frames, andthus, a separate common electric potential portion is not needed.Further, the inductance is decreased by lamination, and thereby, a surgein current or voltage can be effectively prevented.

Especially in the device shown in FIG. 11, the main current paths opposeto each other, and thus, the inductance can be decreased. In the deviceshown in FIG. 12, the elements are disposed in the vicinity of the heatradiating portions, and thus, heat can be effectively radiated from thedevice.

1. A power semiconductor device comprising: a switching powersemiconductor element, and a free wheeling diode in anti-parallelconnection to the switching power semiconductor element, wherein: areverse electrode of the switching power semiconductor element and areverse electrode of the free wheeling diode are bonded and mounted on acircuit pattern formed on a main surface of a first substrate; andprojections, which are formed by projecting parts of a circuit patternso formed on a main surface of a second substrate as to oppose a surfaceelectrode of the switching power semiconductor element and a surfaceelectrode of the free wheeling diode, are soldered and connected to thesurface electrodes of the switching power semiconductor element and thefree wheeling diode, respectively.
 2. A power semiconductor devicecomprising a switching power semiconductor element, and a free wheelingdiode in anti-parallel connection to the switching power semiconductorelement, wherein: a reverse electrode of the switching powersemiconductor element and a reverse electrode of the free wheeling diodeare bonded to a main surface of a first lead frame; and projectionswhich are formed by projecting parts of a main surface of a second leadframe so as to oppose a surface electrode of the switching powersemiconductor element and a surface electrode of the free wheelingdiode, are connected or soldered to the surface electrodes of theswitching power semiconductor element and the free wheeling diode.
 3. Apower semiconductor device according to claim 2, wherein an IC forcontrolling the driving of the switching power semiconductor element ismounted on another surface of the second lead frame, the main surface ofthe second lead frame is opposed to the first lead frame.
 4. A powersemiconductor device comprising a switching power semiconductor element,and a free wheeling diode in anti-parallel connection to the switchingpower semiconductor element, wherein a reverse electrode of theswitching power semiconductor element and a reverse electrode of thefree wheeling diode are bonded to a main surface of a first lead frame;projections which are formed by projecting parts of a main surface of amulti-layer printed board or a through hole board so as to oppose asurface electrode of the switching power semiconductor element and asurface electrode of the free wheeling diode, are connected or solderedto the surface electrodes of the switching power semiconductor elementand the free wheeling diode; and an IC for controlling the driving ofthe switching power semiconductor element is mounted on another surfaceof the multi-layer printed board or the through hole board.